Scientists are puzzled by a new image taken by NASA's Dawn spacecraft, which found two bright spots on the dwarf planet Ceres. The spots are noticeably brighter than other parts of the surface, which looks to be rocky and pockmarked.

As a clinical geneticist, Paul James is accustomed to discussing some of the most delicate issues with his patients. But in early 2010, he found himself having a particularly awkward conversation about sex.

A 46-year-old pregnant woman had visited his clinic at the Royal Melbourne Hospital in Australia to hear the results of an amniocentesis test to screen her baby's chromosomes for abnormalities. The baby was fine — but follow-up tests had revealed something astonishing about the mother. Her body was built of cells from two individuals, probably from twin embryos that had merged in her own mother's womb. And there was more. One set of cells carried two X chromosomes, the complement that typically makes a person female; the other had an X and a Y. Halfway through her fifth decade and pregnant with her third child, the woman learned for the first time that a large part of her body was chromosomally male1. “That's kind of science-fiction material for someone who just came in for an amniocentesis,” says James.

Sex can be much more complicated than it at first seems. According to the simple scenario, the presence or absence of a Y chromosome is what counts: with it, you are male, and without it, you are female. But doctors have long known that some people straddle the boundary — their sex chromosomes say one thing, but their gonads (ovaries or testes) or sexual anatomy say another. Parents of children with these kinds of conditions — known as intersex conditions, or differences or disorders of sex development (DSDs) — often face difficult decisions about whether to bring up their child as a boy or a girl. Some researchers now say that as many as 1 person in 100 has some form of DSD2.

When genetics is taken into consideration, the boundary between the sexes becomes even blurrier. Scientists have identified many of the genes involved in the main forms of DSD, and have uncovered variations in these genes that have subtle effects on a person's anatomical or physiological sex. What's more, new technologies in DNA sequencing and cell biology are revealing that almost everyone is, to varying degrees, a patchwork of genetically distinct cells, some with a sex that might not match that of the rest of their body. Some studies even suggest that the sex of each cell drives its behaviour, through a complicated network of molecular interactions. “I think there's much greater diversity within male or female, and there is certainly an area of overlap where some people can't easily define themselves within the binary structure,” says John Achermann, who studies sex development and endocrinology at University College London's Institute of Child Health.

These discoveries do not sit well in a world in which sex is still defined in binary terms. Few legal systems allow for any ambiguity in biological sex, and a person's legal rights and social status can be heavily influenced by whether their birth certificate says male or female.

“The main problem with a strong dichotomy is that there are intermediate cases that push the limits and ask us to figure out exactly where the dividing line is between males and females,” says Arthur Arnold at the University of California, Los Angeles, who studies biological sex differences. “And that's often a very difficult problem, because sex can be defined a number of ways.”

That the two sexes are physically different is obvious, but at the start of life, it is not. Five weeks into development, a human embryo has the potential to form both male and female anatomy. Next to the developing kidneys, two bulges known as the gonadal ridges emerge alongside two pairs of ducts, one of which can form the uterus and Fallopian tubes, and the other the male internal genital plumbing: the epididymes, vas deferentia and seminal vesicles. At six weeks, the gonad switches on the developmental pathway to become an ovary or a testis. If a testis develops, it secretes testosterone, which supports the development of the male ducts. It also makes other hormones that force the presumptive uterus and Fallopian tubes to shrink away. If the gonad becomes an ovary, it makes oestrogen, and the lack of testosterone causes the male plumbing to wither. The sex hormones also dictate the development of the external genitalia, and they come into play once more at puberty, triggering the development of secondary sexual characteristics such as breasts or facial hair.

Ali and coauthor Saurya Das at the University of Lethbridge in Alberta, Canada, have shown in a paper published in Physics Letters B that the Big Bang singularity can be resolved by their new model in which the universe has no beginning and no end.

We live in a world of illusion. So many of the concerns that occupy the mind and the tasks that fill the calendar arise from planted impulses to become someone or something that we are not. This is no accident.

Feeling a bit nippy? For now you'll have to stick to your hat and scarf to warm up, but one day some antifreeze proteins from a fish or a tick might do the trick.

In a preliminary study published Wednesday in PLOS ONE, researchers report using specially bred mice -- ones spliced with the genes that give ticks antifreeze cells -- to show that mammals can benefit from the proteins that other species use to keep from icing over.

Irish poet William Butler Yeats is perhaps the most well-known member of the Hermetic Order of the Golden Dawn, the influential secret magical society which originated in the late 19th century (and still exists in a number of forms today).

As President Obama seeks $27.6 billion for federal drug control programs in his new budget, we talk to British journalist Johann Hari about the century-old failed drug war and how much of what we know about addiction is wrong.

Cultural beliefs and stereotypes that associate men but not women with “raw intellectual talent” can help explain the differing gender gaps across various academic disciplines, according to a new study by Sarah-Jane Leslie (Princeton), Andrei Cimpian (Illinois, Urbana-Champaign), Meredith Meyer (Ottterbein), and Edward Freeland (Princeton) published today in Science. A similar account appears to explain racial disparities in academia, as well. In short, “the more a field valued giftedness, the f

At the suggestion of appalled supporters, Bonnie Weinstein finally compiled a selection of choice missives into a book, To the Far Right Christian Hater: You can be a good speller or a hater, but you can't be both. I was a conservative Evangelical for many years. Over that time, I imagined saying nasty things to people, and sometimes did. I imagined swearing, and sometimes did. But it never crossed my mind that a believer might combine swearing and denigration with the name of Christ. The kaleidoscope of variations found in Weinstein's book would have been unfathomable. Even today, if I hadn't read them myself, I wouldn't believe it still.

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